1. Field
The following description relates to a method for manufacturing interlayer distance controlled graphene, an interlayer distance controlled graphene composition, and a supercapacitor including graphene with the interlayer distance controlled as an electrode material.
2. Description of Related Art
Graphene is a crystalline allotrope of carbon with two-dimensional properties. Other allotropes of carbon include diamond, graphite, carbon nanotube, bukyball, and the like. Graphene comprises a monolayer of carbon atoms arranged within a pattern of repeating honeycomb lattices in two dimensions. Graphene has attracted attention by researchers by virtue of its electronic, optical, thermal, and mechanical properties. Graphene is utilized on applications to field-effect transistors (FET), memory devices, supercapacitors, transparent electrodes, sensors, and so on. In particular, the utilization of graphene has been studied as electrode materials for electrochemical capacitors (ECs), which are sometimes represented to as supercapacitors or ultracapacitors, due to its large specific surface area, high conductivity, and excellent electrochemical stability.
Graphene can be prepared by various methods such as mechanical exfoliation, chemical exfoliation, chemical vapor deposition, epitaxial synthesis, and the like. Among these methods, the chemical exfoliation is a method of reducing back the graphite derivative after oxidizing the graphite with an oxidizing agent. The chemical exfoliation is a low-cost method and makes it possible to mass-produce graphene, thereby leading to a high possibility of industrial applications thereof. The oxidized graphene has an advantage of being easily utilized with its aqueous dispersibility.
To date, studies have been made on improving the capacity of supercapacitors, in particular, on enhancing the electrical storage capability by increasing effective areas of electrode materials. Electrode materials of supercapacitors that have been marketed are mainly an active carbon, which is insufficient for implementing a supercapacitor with bulk storage since its electrical conductivity is poor and its active areas actually in use are small even though the specific surface area thereof is large. The capacity of the supercapacitor is proportional to the area of an electrode plate. However, when the area increases, the total size of the supercapacitor increases, and hence it is required to maintain an optimum level of the surface area of electrode plate. Under this circumstance, it has been studied to replace the active carbon with carbon nanotubes. In this regard, Korean Patent Application Publication No. 1221979 relates to a method for manufacturing carbon nanotubes applicable to supercapacitors and supercapacitors containing the same. When manufacturing a supercapacitor by using said carbon nanotubes, it is possible to enhance supercapacitor properties by virtue of the excellent conductivity, broad surface area, chemical stability, etc. of the carbon nanotubes. However, the carbon nanotubes have their own limitations in respect that the price is high in itself and it is difficult to manufacture carbon nanotubes with a high quality to a degree suitable for mass production, and so forth.
To this end, studies have been conducted on the application by using graphene having excellent electrical conductivity and specific surface area onto supercapacitors. However, graphene aggregates by itself, and the interlayer distance of graphene is narrow, with approximately 0.35 nm between two layers. Therefore, the shortcoming of graphene is its lack of covering thus-produced electrical charge double layer, at the time of the application of graphene as supercapacitor electrodes.